Protective coatings for wood and various other solid substrates are well known and a wide variety of coating compositions have been used in the past. Some protective coatings serve a number of different purposes such as providing abrasion and scratch resistance and protection against water spotting and solvent damage. Two important types of protective coatings are lacquer-type coatings and reactive-type coatings.
Lacquer-type coating compositions are provided as a solvent solution of solid thermoplastic resins, either naturally occurring resins, e.g., shellac, or synthetic resins, e.g., nitrocellulose. The lacquer-type coating is obtained by coating a substrate with the resin solution and allowing the solvent to evaporate. By using these lacquer-type coating compositions, coatings are obtained that can, in many cases, be sanded, buffed, and polished. The coating, even though it may be somewhat abrasion resistant, is still soluble in certain solvents and therefore, is readily damaged by solvent.
The reactive-type coating compositions are provided as one or more compounds, oligomers, or polymers which contain polymerizable or reactive functional groups such as ethylenic unsaturation, e.g., acrylate or methacrylate groups; epoxy; isocyanate; carboxylic acid; and hydroxyl groups, that can react to chain-extend and/or crosslink to form the protective coating. In some cases, the reaction can take days before the coating has achieved the desired hardness or degree of cure. Compositions containing polymerizable ethylenic unsaturation can be cured by heat or radiation, e.g., ultraviolet light or electron beam radiation. Such compositions cured by ultraviolet light require the presence of a photoinitiator, while those cured with electron beam radiation do not require a photoinitiator. Radiation cured coatings often take only seconds or minutes to cure to yield the final desired properties.
E. Levine in "Formulating Ultraviolet Curable Coatings" (Modern Paint and Coatings, vol. 73, no. 8, 1983, pp. 26-29) discloses radiation curable coatings which contain reactive oligomers, e.g., acrylated epoxies, urethanes, polyesters, and acrylics, multifunctional acrylate and methacrylate monomers, and monofunctional monomers. R. S. Biley in "UV Cured Coatings for Wood Furniture" (Radiation Curing, November 1983, pp. 14-17) mentions unsaturated polyesters and acrylics as UV curable coatings.
Included among prior art radiation curable coatings are the well known polyurethane polyacrylates such as those exemplified in U.S. Pat. No. 4,082,634, 4,097,439 4,233,130 and 4,295,947. Acrylated fatty compounds have also been reacted with polyisocyanates to provide polyurethanes having acrylic and fatty groups for use in radiation curable coatings such as are described in U.S. Pat. Nos. 4,224,369 and 4,233,130.
Polyurethane/urea resins containing pendent cyclic groups are known. For example, in U.S. Pat. No. 3,160,648, the preparation of 9,9-bis(3-isocyanatopropyl)fluorene and its reaction with diols and diamines to form polyurethane or polyurea resins respectively is described. And in U.S. Pat. No. 3,758,422, a polyurethane resin containing a pendent phenolphthalein derivative is described. This resin is prepared by the reaction of a diisocyanate with a phenolphthalein product that had been obtained by reaction of phenolphthalein with ammonia or an amine followed by reaction with a 1,2-epoxide. Also, U.S. Pat. Nos. 4,499,165 and U.S. Pat. No. 4,636,361, disclose mixtures that are more compatible with dyes of non-polymeric oligomers comprising organic nuclei, of which at least one is a multicyclic aromatic nucleus, joined by linking groups that can be an urethane group. In none of these patents is described polyurethane/urea resins having both pendent ethylenically-unsaturated groups and pendent cyclic groups.
Polyethylenically-unsaturated polymers having pendent cyclic groups are known. These polymers can be exemplified by U.S. Pat. No. 4,340,454 wherein it is taught that organic soluble polymers having a glass transition temperature (Tg) greater that 200.degree. C. can be obtained by including in the polymer recurring high-temperature resistant units having a polycyclic structure. Ethylenically-unsaturated polyurethanes or polyureas are not disclosed.
Many polyethylenically-unsaturated polyurethane and polyurea resins are known and can be exemplified by, among many others, U.S. Pat. No. 4,097,439 where radiation curable coating compositions comprising ethylenically-unsaturated polyurethane resins that are the reaction product of polyester or polyether diols with diisocyanates followed by reaction with an ethylenically-unsaturated monoalcohol or monoamine are disclosed. Polymers having pendent cyclic groups are not disclosed.
In none of the patents discussed above or in any others of which applicants are aware are ethylenically-unsaturated polyurethanes or polyureas having pendent cyclic groups disclosed.
Coatings such as these radiation curable coatings are useful in providing various degrees of protection against solvents, stains and abrasions, but all suffer from one or more disadvantages. For example, some coatings prepared from blends of ethylenically unsaturated oligomers and monomers are wet or tacky after coating and thus are susceptible to the pickup of dust particles or foreign matter until crosslinked by radiation. Such coatings do not have a thermoplastic stage that can be sanded and polished. After crosslinking, imperfections which may be present in the insoluble, radiation cured, hard coatings are difficult to correct such as by sanding and buffing, and defects cannot be repaired by removal of the coating by solvents.
Although some of these coatings can be physically worked for various purposes which are conventional to the lacquer art and which can thereafter be exposed to radiation to cure the film to increase the solvent resistance and physical toughness of the film and thereby product a more durable film, there is a need for coatings that provide still better characteristics. Furthermore, the coating compositions may require the use of ethylenically unsaturated isocyanates or low molecular weight ethylenically unsaturated monomers that can cause toxicological problems.
Other deficiencies in many known protective coatings are darkness of coating color and/or lack of clarity, because the coatings include components which are colored or develop color on curing, or are incompatible, i.e., not mutually soluble, with each other.